The contactless smart card is a system being used increasingly in various sectors. In the transport sector, the card has been developed as a means of payment. This is also the case of the electronic wallet. Many companies have also developed identification means for their personnel using contactless smart cards.
The exchange of information between the contactless card and the associated reader is accomplished by remote electromagnetic coupling between an antenna lodged in the contactless card and a second antenna located in the reader. For developing, storing and processing the information, the card is equipped with a chip or an electronic module which is connected to the antenna. The antenna and the chip are typically located on a dielectric support made of plastic material (polyvinyl chloride (PVC), polyester (PET), polycarbonate (PC) . . . ). The antenna is obtained by chemical copper or aluminum etching on the support or winding of conductive metal wire. The chip, including a memory zone and a microprocessor, contains capacitors which define an input capacitance associated with the chip. The optimal operation of the antenna-chip coupling, which must not be resistive, is obtained when the following circuit resonance law is observed:
LCxcfx892=1xe2x80x83xe2x80x83(1)
in which L represents the inductance of the antenna, C represents the input capacitance and xcfx89 the pulse equal to 2xcfx80f, in which f represents the normalized frequency (for example, 13.56MHz).
The obligation to observe this law requires chip manufacturers, also called founders, to integrate adequate capacitors in the chips in order to obtain sufficiently high capacitance values. In this manner, the production cost of the chips is necessarily higher due to the presence of capacitors.
The development of contactless smart cards inevitably includes reducing the production cost of the chips used in these cards. In order to reduce the cost of the chips, founders have been increasingly led to reduce the size of the capacitor built into the chips and to thereby reduce the input capacitance of the circuit. In this manner, manufacturers can produce smaller chips.
In order to observe the law LCxcfx892=1 and to obtain optimal coupling, the inductance L of the antenna has been increased in order to compensate the decrease in the chip""s input capacitance value. In the case of antennas made by using copper or aluminum etching techniques, in the form of turns on a plastic dielectric support, the inductance was increased by augmenting the number of turns. This solution, however, causes several major drawbacks. Indeed, since all electric circuits have a certain resistance, increasing the number of turns, which essentially corresponds to an increase in the circuit""s length, leads to a significant increase in the value of this resistance. This considerably affects the antenna""s performance characteristics and thus that of the card as well. The distance between the reader and the card is reduced significantly.
In order to limit the overall dimensions and to maintain the effective area for the electromagnetic flow through the card, the width of the copper tracks must be reduced. As a result, the resistance of the antenna is increased and, above all, the reliability of the cards is downgraded as there is a higher risk of the antenna turns breaking when the card bodies are subjected to the hot lamination operation under pressure.
The unit cost of the engraved antenna increases considerably. Thus, the cost reductions obtained by the founders with chips having a lower input capacity are cancelled out by the supplementary cost of the antennas. Card fabrication and use are thus not more profitable.
Displacing the capacitance of the chip towards the antenna, by connecting one or more capacitors directly to the antenna is not an acceptable solution either. Traditional capacitors are costly, which does not solve the card cost problem. Furthermore, placing capacitors on the support and connecting them to the antenna is not easy.
The purpose of the invention is to mitigate these drawbacks by supplying an antenna with a parallel capacitance obtained at a lesser cost, thereby obtaining a smart card which is considerably less expensive in relation to the cost of smart cards currently available on the market, owing to the reduction in the number of capacitors in the chip.
The invention thus concerns a coupling antenna connected to an electromagnetic wave transceiver device containing one or several integrated capacitors. This coupling antenna includes at least one screen printed turn on a support consisting of an insulating dielectric support and also includes a screen printed capacitor on the support, connected in parallel, thereby reducing the capacitance supplied by the capacitor(s) built into the device, so that the resulting capacitance forms a resonating circuit with the turn.
The invention also concerns a manufacturing process of this antenna which consists in:
screen printing at least one antenna turn, the lower plate of the capacitor, bonding pads from the antenna to a chip or a module, and the connection from the antenna to the lower plate of the capacitor, by depositing conductive ink onto the support,
performing a second screen print of the capacitor""s insulating strip by depositing dielectric ink, thereby allowing the lower plate of the capacitor to be covered,
performing a third screen printing of the capacitor""s upper plate and the connection of the antenna to the upper plate of the capacitor.